Prepared in cooperation with the

Acid Rain in ,

Visitors to Shenandoah National Park (SNP) enjoy the animal and plant The pH scale is a measure of how acidic (low pH) or alkaline life and the scenery but may not real- (high pH) a solution is. Rainwater is considered normal at 5.6 pH ize how vulnerable these features are to units. Shenandoah National Park rain typically is 10 times more various threats, such as invasion of exotic acidic than normal rain. plants and insects, improper use of park resources by humans, and air and water pollution. The National Park Service rain (currently about 4.6 pH units) falling mic, which means that each whole-num- strives to protect natural resources from onto an environment that has little inher- ber change indicates a 10-fold change in such threats to ensure that the resources ent ability to neutralize the acidic input acidity or alkalinity. For example, a pH of will be available for enjoyment now and and decades of exposure to acid rain have 4 is 10 times more acidic than a pH of 5. in the future. Because SNP has limited resulted in a fragile environment. When Rainwater is considered normal at 5.6 pH influence over the air pollution that the effects of acid rain are combined units; therefore, rain with a pH of 4.6, envelops the region, acidic deposition— with stressors, such as forest defoliation which typically occurs in SNP, is about commonly known as acid rain—is one of caused by the gypsy moth or conifer- 10 times more acidic than normal rain. the more challenging threats facing park ous tree demise caused by the hemlock Acid-neutralizing capacity (ANC)— managers. With the help of U.S. Geo- woolly adelgid, significant environmental the ability of a solution to neutralize logical Survey (USGS) scientists, park problems can develop, and park resources acidic inputs—is a quantitative measure managers can understand how acid rain become threatened. associated with pH (fig. 1). In general, interacts with ground- and surface-water water with a high ANC (for example, resources, which enables them to explain 500 units1) also has a high pH and is why reductions in air pollution can help good at neutralizing acidic inputs. In preserve park resources. Such under- Understanding pH and contrast, water with a low ANC (for standing also provides essential insight Acid-Neutralizing example, 25 units) has a low pH and is into ecosystem processes, as managers a poor neutralizer. Stream animals and strive to unravel and resolve other envi- Capacity plants (the biota) can be sensitive to and ronmental problems that are interrelated negatively affected by changes in ANC, to acid rain. The severity of acid rain and acidic particularly when it decreases to near Even though reductions in emissions streamwater is measured by the pH zero units, which can cause the biota to of acid-forming compounds mandated by scale—a quantitative measure of how suffer “acid shock.” Research on fish the Clean Air Act and Amendments have acidic (low pH) or alkaline (high pH) a indicates that many species are sensitive occurred since 1990, acid rain contin- solution is (fig. 1). A neutral solution, at ANC values less than 50 units. ues to fall in the eastern , which is neither acidic nor alkaline, has including SNP. The combination of acid a pH of 7 units. The pH scale is logarith- 1ANC concentration typically is expressed in microequivalents per liter. “Unit” is used here for simplifying purposes. Acid rain

Fish begin Normal Baking Battery acid Vinegar to die rain soda Ammonia Lye

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Figure 1. Relations Acidic Alkaline of common solutions Neutral and acid-neutralizing capacity to the pH Low acid-neutralizing capacity Intermediate acid-neutralizing capacity High acid-neutralizing capacity scale.

U.S. Department of the Interior Printed on recycled paper Fact Sheet 2007–3057 U.S. Geological Survey July 2007 Shenandoah National Park Streams Acid Rain Facts Shenandoah National Park streams start near the top of a mountain, usually as a spring or seep on a hillface. As the • Acid rain is caused by combustion of fossil fuels (gas, oil, coal) and to a much water flows downhill, the stream increases lesser extent by natural processes (volcanic emissions, forest fires). in size as more tributaries and ground • Combustion emits sulfur dioxide and nitrogen oxides (the two major contributors water contribute to the streamflow. Such to acid rain) into the atmosphere; these oxides can travel hundreds of miles from streams are called “headwater streams.” the source of emission. Because these streams begin with little water, contributions of acid rain can make • Sulfur dioxide and nitrogen oxides convert to sulfuric and nitric acids in the the streamwater more acidic. During atmosphere; the acids are deposited to the earth by wet deposition (rain, snow, storms, acid rain quickly reaches head- fog) and dry deposition (dry particles, gases), collectively referred to as “acidic water streams and can decrease the ANC deposition.” and pH of the stream temporarily. As the pulse of acidic water flows downstream, • Some of the largest emissions in the United States originate in the Ohio River the streamwater recovers to the pre-storm Valley and are carried downwind through the atmosphere toward Shenandoah ANC and pH values. National Park. Although the acidity of rain is spa- • The Clean Air Act, designed to reduce emissions, was passed in 1970, amended tially uniform across SNP, streamwater in 1990, and amended again in 1995. ANC and pH values vary substantially across the park. These differences are • In Shenandoah National Park, the annual average pH values of precipitation related to the underlying geology (bedrock for the following periods were: 4.53 for 1981–1990; 4.59 for 1991–1995; type) and topography (steepness of the 4.62 for 1996–2005. These pH values suggest incremental improvements in slope) of the watersheds. The three main response to the Clean Air Act amendments. bedrock types in SNP are basaltic, granitic, and siliciclastic. Basaltic rocks are the • Rain tends to be most acidic during the summer; longer periods between storms best of the three bedrock types at neutral- allow acids to build up in the atmosphere before being “rained out.” izing acidic inputs, siliciclastic rocks are • Individual pH values of rain well below 4.0 have been measured in Shenandoah poor, and granitic rocks are intermediate. National Park. Each of the three bedrock types underlies approximately one-third of SNP. Shenandoah National Park has 231 headwater streams in which ANC and pH decrease to various degrees, depending on the geology and topography. In general, Streams start as the steeper the slope, the more quickly acid Streamwater Streamwater seeps on a hillface rain reaches the stream with less chance of pH = 6.1 pH = 4.5 ANC = 150 More desirable environment being neutralized along ANC = 5 for fish and other aquatic biota the way. Therefore, a Poor environment for a small stream near the diverse population of fish Streamwater crest of a mountain, pH = 7.2 and other aquatic biota ANC = 250 on a steep slope, and Soil underlain by siliciclas- tic bedrock, is likely Basaltic Bedrock to have some of the Streamwater most acidic water in pH = 4.6 Siliciclastic Bedrock ANC = 15 SNP (fig. 2). Such streamwater does not support a diverse popu- lation of aquatic biota. Conversely, a large stream with a gentle slope and underlain by basaltic bed- Figure 2. Two stream systems with different characteristics that result in differences in water quality. rock will have near-neutral Whether or not the aquatic biota will be diversified is strongly controlled by the geology and topography. water and, consequently, a diverse population of aquatic biota (fig. 2). Front Royal Entrance Station Front Royal Washington, D.C.

Shenandoah Dickey Ridge Visitor Center Waynesboro National Park

CHESAPEAKE

Richmond Mathews Arm

BAY 78o15'

VIRGINIA ATLANTIC OCEAN

38o45' Elkwallow Shenandoah National Park Facts

Skyline Drive • Consists of 308 square miles (nearly Entrance Station 200,000 acres) • Straddles the crest of the Panorama • Stretches from Front Royal in the north to in the south, with traversing the entire length Skyland • Touches eight counties (Albemarle, Augusta, Byrd Visitor Center Greene, Madison, Page, Rappahannock, 78o30' Rockingham, and Warren) 38o30' • Has 231 headwater streams Big Meadows

• Contains three main types of bedrock Skyline Drive (basaltic, granitic, and siliciclastic) Lewis Mountain • Has land-surface elevations that range from about 600 to 4,051 feet Entrance Station

78o45'

EXPLANATION MINIMUM ANC VALUES 38o15'

Skyline Drive Less than or equal to 50 units (poor ability to neutralize acidity) Loft Mountain Greater than 50 units (better ability to neutralize acidity) Shenandoah National Park boundary Watershed boundary

0 5 10 MILES

0 5 10 KILOMETERS

Rockfish Gap Entrance Station

Figure 3. Predictions of Shenandoah National Park watersheds that are likely to have a minimum average acid-neutralizing capacity (ANC) less than or equal to 50 units (red) or greater than 50 units (blue) for 6 consecutive hours about once every 4 years. The watersheds shown in red have the greatest likelihood of losing native aquatic species because of extended periods of low ANC. Models and Predictions These results are of concern because Scientists studied streamwater data from five SNP streams and developed a they indicate a high probability for loss specific mathematical model for each of of native aquatic species in the park. the five watersheds based on mathemati- cal relations among ANC decreases in each stream and the geologic and topo- graphic characteristics of the watershed One-half of the SNP watersheds are For additional details about the (Rice and others, 2005). The models for predicted to have ANC values less than or information presented here, refer to the five watersheds were transferred to equal to 50 units for 6 continuous hours Rice, K.C., Deviney, F.A., Jr., Horn- the rest of the watersheds on the basis of approximately once every 4 years. This berger, G.M., and Webb, J.R., 2005, known geology and topography in each does not mean that the other half of the Predicting the vulnerability of streams watershed. SNP watersheds will never have these to episodic acidification and potential The models were designed to predict same conditions, but the probability of effects on aquatic biota in Shenandoah the magnitude, frequency, and duration having them in any given year is pre- National Park, Virginia: U.S. Geologi- of decreases in ANC in each of the 231 dicted to be less than 25 percent. cal Survey Scientific Investigations streams. The magnitude of a decrease Report 2005–5259, 51 p. (online at in ANC is important because as water http://pubs.water.usgs.gov/sir2005- approaches zero units, fewer fish spe- Fish Health Threatened 5259/). cies are able to tolerate the increased acidity. The frequency of a decrease Of the 231 SNP watersheds, 52 are Mission of USGS: The USGS serves the in ANC is important because the more predicted to occasionally have 3-day Nation by providing reliable scientific often the ANC changes, the less time periods when the average ANC value is information to describe and understand the aquatic biota has to recover between less than zero units, and 34 of these will the Earth; minimize loss of life and prop- storm events. For example, during the have less than 2 years between occur- erty from natural disasters; manage water, spring when many fish spawn and other rences of this condition. These predic- biological, energy, and mineral resources; organisms reproduce, fish larvae and tions indicate that within the next 40 to and enhance and protect our quality of young fry are especially sensitive to acid 100 years, these 34 watersheds will have life. shock. Two back-to-back events caus- 4 consecutive years when this condition ing streamwater to have zero units ANC occurs at least once each year, assum- Mission of NPS: The NPS preserves could destroy an entire population of ing there is no change in the current unimpaired the natural and cultural aquatic organisms. The duration of a resources and values of the national decrease in ANC is important because park system for the enjoyment, edu- aquatic biota may be able to survive acid cation, and inspiration of this and shock for a short time, but the longer the future generations. The Park Service water remains acidic, fewer organisms cooperates with partners to extend the will survive. benefits of natural and cultural Predictions of annual minimum resource conservation and outdoor ANC values for specific durations that recreation throughout this country could occur on average once every and the world. 4 years for each of the 231 watersheds are summarized on maps of SNP. These Brook trout in Shenandoah National Park For information about Shenandoah predictions were made for 6-hour, 1-, 3-, National Park, see http://www.nps. and 7-day durations. The 6-hour dura- gov/shen/index.htm tion map (fig. 3) indicates the watersheds (2007) acid rain conditions. The prob- that are predicted to have a minimum ability for these predictions to be accurate average ANC value less than or equal is greater than 90 percent. Several fish to 50 units (red) or greater than 50 units species, including native brook trout (the (blue) for 6 continuous hours during any most acid-tolerant species in SNP), have For information about water resources 4-year period. During the 6 hours, ANC maximum life spans less than 4 years. in Virginia, see http://va.water.usgs.gov values may increase or decrease, but the Less acid-tolerant species, such as rosy- or contact Mark Bennett, Director, average ANC value for the 6 hours will sided dace, are even more vulnerable. U.S. Geological Survey Virginia Water be lower than for any other 6-hour period. Science Center, 1730 East Parham Rd., Stated another way, the map indicates the Karen C. Rice, Frank A. Deviney, Jr., Richmond, VA 23228; 804-261-2643 watersheds that are predicted to have a and Gordon Olson ([email protected]). 25-percent chance in any single year to have a minimum ANC value less than or equal to 50 units for 6 continuous hours.